When attempting to vary the direction of maximum radiation or side lobe characteristic of an array antenna by appropriately controlling the driving phase of each of a plurality of radiating elements forming the array antenna, or when attempting to realize a high-output transmitting device by parallel-operating a plurality of transmitters and controlling the output phase of each transmitter such that each is the same phase, line stretchers constructed so as to mechanically vary the length of the transmission line of a signal, or waveguide-type phase shifting devices formed by inserting a dielectric plate within a waveguide have conventionally been used.
FIG. 1 presents several views of a waveguide-type phase shifting device of the prior art, FIG. 1A showing a plan view, FIG. 1B showing a side view, FIG. 1C showing a sectional view taken at the B--B line of Fig. 1B, and Fig. 1D showing a sectional view taken at the A--A line of FIG. 1A.
In rectangular waveguide 11, flanges 12.sub.1 and 12.sub.2 are provided for inserting and connecting such a waveguide-type phase shifting device within a rectangular waveguide circuit. A dielectric plate 13 is provided within rectangular waveguide 11 such that the plate surface is parallel to the electric field within the waveguide 11. As shown in FIG. 1D, the contour of this dielectric plate 13 is formed as a parallelogram, this parallelogram having inclines on the edges of the radio-wave incident side and edges of the opposite side which are formed so as to improve the radio-wave reflection characteristic at these edge portions.
Instead of providing inclines to the edges of the radio-wave incident side and edges of the opposite side of this dielectric 13, the radio-wave incident portion and opposite side portion of the dielectric 13 may be formed such that the plate thickness gradually varies.
Support fittings 14.sub.1 and 14.sub.2 for dielectric plate 13 pass through the opposing short sides of rectangular waveguide 11 and dielectric plate 13. Support fittings 14.sub.1 and 14.sub.2 may freely slide at the portions where they pass through the opposing short sides of rectangular waveguide 11 but are secured to the portions where they pass through dielectric plate 13.
Coupling plate 15 links together support fittings 14.sub.1 and 14.sub.2. This coupling plate 15 serves as a handle for moving support fittings 14.sub.1 and 14.sub.2 either forward or backward in the axial direction of each of support fittings 14.sub.1 and 14.sub.2 while maintaining dielectric plate 13 in the attitude shown in Fig. 1D, thus allowing the plate surfaces of dielectric plate 13 to be moved from a position coinciding with the central axis in the longitudinal direction of rectangular waveguide 11 to a position close to either of the opposing short sides as shown in FIG. 1C, thus enabling variation in the proportion of shift change of radio waves propagated through rectangular waveguide 11.
In other words, such a phase shifting device uses the change in propagation speed of radio waves within rectangular waveguide 11 according to the dielectric constant, thickness, and length in the direction of wave propagation of dielectric plate 13. When interposed at a position coinciding with the central axis in the longitudinal direction of rectangular waveguide 11, where the electric field intensity is at maximum strength, dielectric plate 13 exercises a large effect upon the propagation speed of radio waves, but the electric field strength progressively weakens with distance from the longitudinal central axis of the rectangular waveguide 11 and proximity to either of the short sides, and consequently, as the position of insertion of dielectric plate 13 shifts away from the central axis of rectangular waveguide 11 and approaches either of the short sides, the effect upon the propagation speed of radio waves decreases. Accordingly, the degree of phase shifting can be varied by changing the position of insertion of dielectric plate 13.
Support fittings 14.sub.1 and 14.sub.2 are maintained parallel to each other, their relative spacing (spacing in relation to the longitudinal direction of rectangular waveguide 11) being selected as .lambda..sub.g /4 (.lambda..sub.g is the wavelength within the waveguide corresponding to the employed frequency), whereby reflected waves arising at the support fitting 14.sub.1 closer to the radio-wave-incident portion and reflected waves arising at support fitting 14.sub.2 which travel back to the position of support fitting 14.sub.1 are of mutually reversed phase and cancel each other, thereby enabling an improved reflection characteristic.
A line stretcher used in the prior art must regulate the line length according to the required degree of phase shifting, and therefore, when the required degree of phase shifting is great, not only is a large-scale mechanical structure required, but a relatively time-consuming and labor-intensive adjustment is required to accurately match the line length with the degree of phase shift.
The waveguide-type phase shifting device shown in FIG. 1 involves the drawbacks that a long dielectric plate 13 is required when a large amount of phase shift is called for, resulting in a phase shifting device of large overall size, and that a great deal of time and effort is required to adjust the insertion point of the dielectric plate 13 to accurately match the amount of phase shift with the required value.
FIG. 2 shows a power supply circuit configured using phase shifting devices of the prior art for controlling the driving phase of subarray antennas and for varying the direction of maximum radiation as well as the side lobe characteristic of an array antenna. This power supply circuit is configured from subarray antennas 16.sub.1 -16.sub.4 each composed of a plurality of element antennas, phase shifting devices 17.sub.1 -17.sub.3 of the above-described prior art, transmission lines 18.sub.1 -18.sub.3 having a degree of phase shift that serves as a standard, and two-branch circuits 19.sub.1 -19.sub.3.
A phase shifting device of the prior art not only entails the same drawbacks as the above-described line stretcher, but when used as shown in FIG. 2, in which a power supply circuit is configured for varying the direction of maximum radiation or side lobe characteristic of an array antenna, further entails the drawback of complex structure of the power supply circuit due to the need for transmission lines 18.sub.1 -18.sub.3 having an amount of phase shift that serves as a standard and two-branch circuits 19.sub.1 -19.sub.3 for phase shifting devices 17.sub.1 -17.sub.3, respectively.